Cyclotriphosphazene-Based Intumescent Flame Retardant against the Combustible Polypropylene

Flame retardant polypropylene (PP) was obtained through appropriately blending with microencapsulated ammonium polyphosphate (MAPP) and a novel cyclotriphosphazene-based char-forming agent (CPCFA) and synthesized using a one-pot method in high yield (86.5%). An increase in the limiting oxygen index (LOI) and the observation of a vertical burning (UL-94) V-0 rating as well as the reduction of the heat release rate (HRR) and residual mass of PP/MAPP/CPCFA blends compared to those for PP/MAPP demonstrated the effectivess of a contribution of MAPP and CPCFA to PP in flame PP. Thermogravimetric analyses results demonstrated that the presence of CPCFA improved char formation for PP/MAPP/CPCFA blends in either nitrogen or air atmosphere. Finally, an outstanding water resistance was also obtained for compositions in the weight ratio range of 3:1 to 2:1 (MAPP/CPCFA). After water soaking for 72 h, a UL-94 V-0 rating was still achievable.